Relapse Prophylaxis Post-Haploidentical Bone Marrow Transplantation and Cyclophosphamide (Haplo/Cy) By Infusion of Donor-Derived Expanded/Activated Gd T Cells: A Phase I Trial

Background: Effector γδ T cells immediately recognize and kill malignant cells in a broad-based non-MHC restricted manner. Increases in circulating donor-derived γδ T cells during post-bone marrow transplant (BMT) recovery have been significantly associated with improved disease-free survival (DFS). Relapse post Haplo/Cy BMT occurs in approximately 45% of patients. We sought to mitigate relapse in this context by expanding, activating, and infusing donor-derived haploidentical γδ T cells. We now report preliminary clinical and biologic correlative findings from the first cohort of patients who have been treated with ex vivo expanded and activated donor γδ T cells (EAGD). This single-center Phase I clinical trial represents the first systemic infusion of allogeneic EAGD cells in the post-BMT setting

Methods: Standard of care reduced-intensity flu/cy/TBI conditioning was followed by an unmanipulated bone marrow graft and 50mg/m² Cy on days +3 and +4 post-transplant. EAGD were manufactured using the Miltenyi Prodigy bioreactor and cryopreserved. The product was infused intravenously within 5 days of neutrophil engraftment (ANC >500/µL X 3d). Peripheral blood was collected at EAGD infusion and monthly thereafter through day +90, with additional collections every 6 months through 1 year. Biologic parameters included multiparameter flow cytometric immunophenotyping and single cell cytokine analysis of the EAGD graft. Peripheral blood analysis includes leukocyte count and differential, immunophenotyping, and serum Th1/Th2/Th17 cytokine analysis. Primary endpoints include dose-limiting toxicities (DLT) and grade 3-4 adverse events while secondary endpoints include incidence of acute and chronic GvHD, relapse, and overall survival.

Results: Three patients have received the first dose level of 1 x 10⁶ EAGD/kg. All three patients remain in morphologic complete remission at 26.5, 24.2, and 12.5 months post-BMT. One patient is receiving ongoing hypomethylating therapy for the occurrence of recipient chimerism. Grade 1-2 toxicities include constipation, CMV reactivation, emesis, fatigue, and hypomagnesaemia. Steroid-responsive cutaneous acute Grade I-II GVHD has been observed in all patients with one patient experiencing Grade II intestinal GvHD. No chronic GVHD, DLTs, treatment-related ≥ grade 3 adverse events, or cytokine release syndrome has occurred. EAGD grafts contained 88.7% - 99.2% Vγ9Vδ2+ γδ T cells with small populations of NK cells and <1.0 x 10 αβ T cells/kg. EAGD principally expressed Granzyme B, MIP1α, MIP1β, and IL-2.

Significant peripheral lymphodepletion persisted through the first 100 days post-BMT followed by slow recovery of CD4+, CD8+, γδ T and B cells. NK cells remained within the low normal range throughout. T cells transitioned from a CD45+CD27- effector phenotype to CD45RA CD27 central to effector memory phenotype as recovery progressed. CD3 CD4 CD25 FoxP3 Treg cells remained <3% of circulating T cells. Preliminary serum cytokine and chemokine analysis revealed predominant expression of IFNγ, IL-12p70, IP-10, RANTES and TNFα.

Conclusions: Early indications suggest that EAGD transfusion with the initial dose level of 1 x 10⁶ EAGD/kg has manageable toxicity and an appropriate immune recovery profile with 3 of 3 patients alive and progression-free.

Clinical Trial Registry: https://clinicaltrials.gov/ct2/show/NCT03533816